How to make curved (bent) rectangle, and add material?
The shape of the object.




Cube scaled as appropriate in Edit Mode
Loop Cut to provide vertex density to allow the next step to work.  The edges are shown above.
Curve Modifier.
Smooth Shading
Edge Split Modifier to keep sharp corner where needed and keep smooth shading where needed
I hesitate to comment on material yet I will comment that the dark lines can be achieved with Freestyle which requires more searching and learning.


You can search [Curve Modifier] and [Edge Split].  There will be many matches at BSE.

Hopefully you get more than one answer with different approaches as well.